The invention pertains to oil primary controls for oil-fired heating systems, and in particular, to an improved lockout mode control for an oil primary.
Oil heating systems employ a control, referred to generally as an oil primary, which controls the delivery of a fuel oil/air mixture and ignition spark to the combustion chamber of the oil burner. Such systems also use a combustion or flame detector, usually a photosensor, to detect when combustion has successfully begun. This is necessary because, for a number of reasons, it is possible that an attempted ignition may not result in combustion. Such factors include a complete or partial loss of fuel or air, loss of ignition source, or clogged or failed component in the oil burner. One function of the oil primary is to interrupt the flow of oil to the combustion chamber if successful combustion is not detected within a certain time period, which is often referred to as the lockout time or the TFI (trial for ignition) time. If combustion is not confirmed within the lockout time, the oil primary shuts off the flow of oil and air, and igniter spark, and places the system in lockout mode. In lockout mode, the system will no longer respond to a call for heat from a thermostat, which it would do, of course, in a normal mode of operation.
Normally, manual intervention is required to take the system out of lockout mode, either by a service person or by the homeowner/user. A reset button is provided in association with the oil primary to allow user activation of a reset input. Alternatively, it is envisioned that suitable intervention may be provided remotely via a communication link. Since it is possible that the problem which caused the lockout may self-correct, the reset gives the opportunity of successfully starting the oil heating system again. If the restart attempt is successful, it avoids the inconvenience and expense of a service call, and in the worst case, may avoid the prospect of frozen or damaged pipes in the home.
However, if the root problem which caused the lockout has not cleared or is not fixed, a reset will cause another attempted oil ignition cycle, and result in a further lockout. In many instances a homeowner may continue to push the reset button, in an attempt to restart the system. In cases where the system does not clear or correct itself, this will result in flooding of the combustion chamber with unignited oil. This might create a hazard, and may require a service person to come to the site and clean out the combustion chamber, which is a time consuming and costly process. Because of these problems, prior oil primaries, such as the Model R7184 Interrupted Electronic Oil Primary commercially available from Honeywell International Inc., have generally provided a limitation on the reset function, for example, limiting it to three times without successful ignition, after which the system remains in lockout and a service person must be called. This approach has the disadvantage, however, that if service is not readily available during cold periods, occupants may not be able to continue living in the space to be heated, and under certain. circumstances, damage may result due to freezing water pipes.
The present invention improves on the lockout control of the prior art by allowing flexibility and a greater number of user resets and ignition retries in the event of lockout, while still minimizing the unwanted accumulation of oil in the combustion chamber.
According to the present invention, if lockout occurs due to failure of combustion to take place, the oil primary is placed in a restricted mode of operation in which a limited number of reset activations may be attempted. If they are unsuccessful, a waiting time interval is imposed between successive attempts, and optionally the lockout time is also reduced for such subsequent attempts, to minimize flooding. Normal operation is returned once a successful combustion cycle has been achieved.
According to the present invention, there is provided an oil primary for initiating and controlling oil combustion in an oil heating system, normally in response to a thermostat or Aquastat(copyright) signal indicating a call for heat. An ignition detector, such as a Model C554A Cadmium Sulfide Flame Detector commercially available from Honeywell International Inc., provides an indication to the oil primary of whether or not combustion has been achieved in the oil heating system. If combustion is not detected within the lockout time period, oil is shut off and the system is placed in lockout mode. A user reset is provided for receiving user reset inputs, which release the lockout mode to permit the oil primary to retry combustion. In the event of a number of such retries without successful combustion, the system imposes a waiting interval before permitting a further retry in response to a user reset activation.
According to another feature of the invention, after a number of unsuccessful retries, the lockout time period is reduced, to reduce the amount of oil introduced into the combustion chamber on each retry, to further reduce the possibility of oil flooding.